Abstract: Objective To investigate the response of astrocytes and neurons in the medullary visceral zone (MVZ) to neuropathic pain induced by the spared nerve injury (SNI, the tibial nerve and the common peroneal nerve were sectioned, while the sural nerve was intacted). Methods The SNI operation and sham operation (only incised the skin of thigh, but the tibial nerve and the common peroneal nerve did not cut) were performed in adult male Sprague-Dawley rats. The paw withdrawal mechanical threshold (PWMT) was measured at 10,20,30 days after operation. By using single or double immunofluorescent staining method，we investigated and measured that the mean fluorescent intensity (MFI) of anti-glial fibrillary acidic protein (GFAP, a marker of astrocytes) signal in the astrocytes, the mean member of Fos/ GFAP double labeled astrocytes and Fos / tyrosine hydorxylase (TH) double labeled neurons in MVZ after operation. Results As compared with control or sham groups, SNI induced that the PWMT became significant sensitivity and peaked at 20 days after SNI. The activated astrocytes revealed an activated morphology, the MFI of anti-GFAP signal markedly strengthened, the mean number of Fos/GFAP double labeled astrocytes and Fos/TH double labeled neurons in the nucleus of the tract solitarius (NTS) and the ventral lateral medulla (VLM) increased significantly and peaked at 20 days after SNI. Conclusion The neurons and astrocytes in MVZ were sensitively activated by SNI.

Key words: Neuropathic pain, Meduallary visceral zone, Neuron, Astrocyte, Nucleus of tract solitarius, Ventral lateral medulla, Immunofluorescent, Rat